The present invention relates generally to processing of wastewater onboard a marine vessel, involving flashing of the wastewater into water vapor.
Presently, liquid waste in the form of bilgewater is cleansed by processing systems which utilize ultrafiltration membranes to separate oil and water, as disclosed for example in U.S. Pat. No. 5,932,091 to Tompkins et al. Such processing systems rely on fine-sized membrane pores which create high fouling rate problems so as to require use of flushing modes and heavy duty recirculating pumps to wash membrane surfaces in order to prolong membrane life. It is accordingly, an important object of the present invention to provide a processing system for cleansing wastewater such as oily bilgewater that avoids reliance on ultrafiltration membranes subject to fouling and an unduly shortened life in the absence of extensive back flushing operational modes.
In accordance with the present invention, wastewater is processed in a flash chamber under vacuum established within an upper section thereof by a vacuum pump. Before delivery to the flash chamber, the wastewater is preheated in a heat exchanger to enhance subsequent flashing thereof effected by entry through an orifice. Water vapor produced by such flashing rises into and fills the upper chamber section, while liquid waste oil droplets are deposited into a bottom section of the flash chamber. A de-mister filters out contaminants from the rising water vapor entering the upper section of the flash chamber and liquefied water vapor is collected therebelow during removal of such rising water vapor from the flash chamber in a superheated or saturated condition for condensation by cooling. The water condensate and the waste oil are respectively withdrawn by distillate and drain pumps under automatic level sensing switch controls. The water condensate withdrawn by the distillate pump is conducted through an oil content monitor for overboard discharge from a distillate tank, while the waste oil or contaminants from the bottom of the flash chamber is delivered by the drain pump to a waste storage tank to which the water condensate is delivered when an excessive amount of contaminant is detected therein. Level sensors associated with the automatic pump drive controls shut down the distillate pump when the water condensate within the distillate tank drops below a predetermined level. On the other hand, the drain pump is turned on and off automatically under level sensor control in order to prevent it from running dry and to maintain the vacuum inside the flash chamber. An alarm is activated by a pressure sensor to alert the operator when the vacuum in the flash chamber is lost. When the desired vacuum pressure is attained for flashing to occur, the vacuum pump is automatically turned off under pressure control by the flash chamber pressure sensor.
Pursuant to one embodiment of the invention, processing involves use of a condenser to cool and condense the superheated and compressed water vapor withdrawn from the flash chamber. Heat is transferred to the incoming wastewater during its initial passage in a heat absorber coil through the rising water vapor within the lower section of the flash chamber. The wastewater is then conducted from the condenser to the heat exchanger to undergo preheating before delivery to the entry orifice in the flash chamber.
A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:
A schematic diagram depicts a wastewater processing system in accordance with one embodiment of the present invention, showing various components of the system interconnected by operational circuitry.